In an e-mail Sunday, Twitter is alerting its members to changes to its policies on privacy and service usage, including support for Do Not Track, as well as informing them about a new weekly digest of interesting news and items from their feeds.

"New things are always happening here at Twitter HQ," the e-mail says. "We're growing at a rapid pace, and our commitment to simplicity, transparency, and reaching every person on the planet continues."

In the service's privacy policy, it's offering more detail -- in plain English -- about what information it collects. Not only does it collect information when you register with Twitter, but also profile information you post to your account.

"Our Services are primarily designed to help you share information with the world," Twitter explains. "Most of the information you provide us is information you are asking us to make public. This includes not only the messages you Tweet and the metadata provided with Tweets, such as when you Tweeted, but also the lists you create, the people you follow, the Tweets you mark as favorites or Retweet, and many other bits of information that result from your use of the Services."

Twitter also collects "log" information about you when you use the service or its widgets. That includes your IP address, browser type, operating system, referring web page, pages visited, location, your mobile carrier, device and application IDs, search terms, and cookie information.

Log information is purged after 18 months of collection, Twitter says; and after a maximum of ten days, Twitter will start to delete or aggregate your widget data, a process that's usually instantaneous, but can take up to a week.

The service also noted that it is supporting the Do Not Track (DNT) function found in a number of web browsers. Browsers supporting DNT include Firefox 5.0+, Microsoft Internet Explorer 9.0+, Apple Safari 5.1+, and Chrome 17.0+ with a third-party extension.

When DNT is activated, Twitter will stop tailoring your account based on the places you visit on the Web that have Twitter buttons on them. What's more, tailoring will be shut off by default if you have DNL activated when you join the service or if it was activated before the tailoring feature was launched. You can also shut off tailoring manually through your account settings.

Twitter clarifies its explanation of how it shares data. For instance, it will share data you give it permission to share, or when the data is not private or personal.

It will also share data to protect the safety of a person, to counter fraud and protect system security, and to comply with requests from law enforcement and regulators.

However, that doesn't mean the service will roll over for the law whenever it comes knocking at the door, as is being illustrated in a recent case involving a protester in New York City. In that case, Twitter is refusing to turn over to prosecutors the tweets of Malcom Harris, who was among a group of demonstrators arrested in October 2011 for marching on the roadway of the Brooklyn Bridge. Twitter has been ordered by a court to turn over the tweets, but it's appealing that decision.

Twitter's weekly digests

Twitter also notes in its letter to members that it will be rolling out over the next few weeks a feature that sends weekly digests of tweets from your Twitter feed that the service thinks you may have missed and will be interesting to you. Also in the digests will be the "most engaging tweets" seen by the people you follow.

The digests will be interactive. You'll be able to click a headline in the digest to go to its source online, for example, as well as view the details of an item, retweet or "favorite" it, or view the conversation it's in.

Given how overwhelming Twitter feeds can become, the digests, if the algorithm that creates them truly identifies worthwhile content, could be a welcome addition for many Twitter users.